Found two Robert Johns one if reference 1234 and the other 970075 but the site wont let me get any further information
They were Gunners in the Royal Field Artillery
Let me try and walk you through this.
- Only a fraction of WW1 British army service records survive, due to fire in WWII. So chances are his records don't exist ant more.
- The British Army was not exactly consistent in how records were indexed. If your grandad was Robert John, possibly known by John, then he could appear under any of the following:
* Robert John
* Robert
* John
* R J
* R
* J
So, the only way you can tell if either of the two records you found is actually your grandfather is to pay up, and download! The search listing is just not sufficient. I would note that the same service records are also held by Ancestry, and probably FindMyPast. Some libraries have subscriptions.
On the other hand, if he continued to serve after some time in 1920 (I don't know the exact date), then his records will have survived. If so, they are still held by the British Ministry of Defense, and have not been made public. You would have to make a personal application.